Alarm latching circuit

ABSTRACT

A REMOTE CONTROL CIRCUIT FOR A D.C. ACTUATED ALARM APPARATUS HAS BEEN PROVIDED WHICH INCLUDES A COIL, AN ARMATURE ACTUATED IN RESPONSE TO ENERGIZATION OF THE COIL, A NORMALLY CLOSED SET OF SPRING BIASED BREAKER POINTS SERIALLY COUPLED TO THE COIL AND OPENED BY THE ACTUATION OF THE ARMATURE. AN IMPEDANCE BRIDGES THE POINTS FOR MAINTAINING CIRCUIT CONTINUITY REGARDLESS OF THE CONDITION OF THE POINTS. AN ALARM CONDITION SENSING MEANS COMPLETES THE CIRCUIT IN RESPONSE TO THE ALARM CONDITION. A NORMALLY NON-CONDUCTIVE TRIAC SEMI-CONDUCTOR HAS ITS MAIN CONDUCTION PATH SERIALLY COUPLED WITH THE COIL AND ITS GATE ELECTRODE COUPLED TO THE ALARM CONDITION SENSING DEVICE FOR TRIGGERING CONDUCTION OF THE TRIAC AND ACTUATING THE COIL IN RESPONSE TO SAID CIRCUIT COMPLETION.

Dec. 12, 1972 c. BERNS ALARM LATCHING CIRCUIT Filed Feb. 19, 1971 -00WARNING DEVICE no) FIG. 1

FIG. 2

. tively bulky,

United States Patent US. Cl. 340-213 R 3 Claims ABSTRACT OF THEDISCLOSURE A remote control circuit for a DC. actuated alarm apparatushas been provided which includes a coil, an armature actuated inresponse to energization of the coil, a normally closed set of springbiased breaker points serially coupled to the coil and opened by theactuation of the armature. An impedance bridges the points formaintaining circuit continuity regardless of the condition of thepoints. An alarm condition sensing means completes the circuit inresponse to the alarm condition. A normally non-conductive triacsemi-conductor has its main conduction path serially coupled with thecoil and its gate electrode coupled to the alarm condition sensingdevice for triggering conduction of the triac and actuating the coil inresponse to said circuit completion.

BACKGROUND OF INVENTION This invention relates to control apparatus fora warning device and in particular to a remote control circuit for adirect current actuated magnetic alarm apparatus.

When considering the manufacture of a production item having arelatively low selling price, such as a door bell, obviously one of themost important considerations would be the production costs of such anapparatus. In this connection, simplicity of operation, long life, andease of manufacture all have a direct bearing on the ultimate cost ofthe article and must be carefully considered before a decision toproduce large numbers of such items is made. A DC. hell or buzzer devicerequires at the very least a source of power; for example, a battery,and a coil, an armature activated by the coil, and a set of springbiased breaker points periodically opened by the energization of thecoil for returning the points back to a closed condition, againpermitting energization of the coil. If a remote control were required,then perhaps a switch operated by a sensing device would be actuated inresponse to an alarm condition and such actuation would energize a relayat the device to close the circuit and provide a warning by energizingthe bell. However, the requirement for a relay in a production time,many times proves too costly and other means are sought out. In additionto the cost of the item, a relay may be relarequire more power tooperate, than is desirable, and not last as long as a solid stateswitching device. Other disadvantages further include the problems ofmounting the relay within the housing and in many cases, polarityconsiderations must be taken into account before the final electricalconnections are made with some relays and generally with mostsemi-conductor switches.

It is therefore an object of the present invention to provide a systemwhich obviates one or more of the disadvantages of the described priorarrangements.

It is another object of the present invention to provide a systemutilizing a simply installed and relatively inexpensive switchingdevice.

It is another object of the present invention to provide a simplifiedremote control circuit for a direct current actuated electro-magneticalarm apparatus.

SUMMARY OF THE INVENTION There has been provided a remote controlcircuit for a direct current actuated electro-magnetic alarm apparatusincluding a coil and armature actuated in response to energization ofthe coil. Normally closed spring biased breaker points serially coupledto the coil are opened by the actuation of the armature and an impedanceis coupled across the points for maintaining circuit continuityregardless of the opened or closed condition of the points. An alarmcondition sensing device provides a complete circuit in response to analarm condition and a normally non-conductive triac semi-conductor hasits main conduction path serially coupled with the coil and its gateelectrode coupled to the alarm condition sensing device for triggeringconduction of the triac and actuating the coil in response to saidcircuit completion.

For a better understanding of the present invention together with otherand further objects thereof, reference is had to the followingdescription taken in connection with the accompanying drawings, whileits scope will be pointed out in the appended claims.

FIG. 1 is a schematic drawing of the circuit of the present invention.

FIG. 2 is a schematic drawing of the essential make-up of a triac.

DESCRIPTION OF TI-H3 PREFERRED EMBODIMENT FIG. 1 shows a D.C. warningdevice 10 any suitable bell or buzzer arrangement which operates from adirect current source. A source of DC. energy; namely, a battery 11energizes a circuit including a main power switch 12, a fuse 13, anormally non-conductive triac 14, an inductive coil 15, and a set ofnormally closed breaker points 16 completes the circuit to ground.Resistor 17 is included in order to maintain continuity of the circuitregardless of the opened or closed condition of the breaker points 16and its function will be explained later in the discussion. A set ofremote switches S1 through Sn are located at various points in aspecific area or as required and the closure of any one of theseswitches S1 through Sn causes an energization of the circuit as follows.The triac 14 has a gate electrode G, shown in the drawing, and conductsin the direction of the forward current depending upon the biascondition of the gate G. Under the conditions set forth in the drawing,a grounding of gate G causes the triac to conduct energizing the coil 15which in turn operates an armature in the warning device 10 whichstrikes a bell, gong or other suitable noise making apparatus. Inaddition the armature opens breaker points 16 which deenergizes coil .15and allows breaker points 16 to close and again cause energization ofthe coil 15 provided the triac 14 is still conducting. Since the triac14 is a semi-conductor device, it requires some stable bias to provide areliable operating point. In this case the battery 11 provides a biasacross the triac 14 and the resistor 17 maintains a bias level for thetriac 14 such that once it is conducting, it remains conducting unlessthe main current path is interrupted as for example by opening theswitch 12. For this reason, the resistor 17 is placed across the breakerpoints so that regardless of their opened or closed condition, the triacalways carries sufiicient holding current as established by the resistor17 so that it remains conductive as long as its forward bias conditionstill exists. Resistor 17 may also be used for supervisory purposes.

It is conceivable that a silicon controlled rectifier can take the placeof the triac 14. However, there are reasons why this is not provided inthis disclosure as described in accordance with FIG. '2. The drawingshows the basic or essential make-up of a triac. It includes two SCRscoupled in parallel in an inverse fashion with common which may begates. Under these conditions, the triac can conduct and block currentin both directions in accordance with the condition of the common gateGC. If a positive bias is placed across SCR 1 and it is steadilyincreased,' eventually an avalanche occurs and SCR 1 goes into a highconduction state. The bias required to drive SCR 1 to a conducting stateis inversely related to the potential applied to the gate GC. As thegate current increases, the bias required to drive SCR 1 intoconductance decreases.

Once the SCR has been triggered in the forward direction, the gate G hasno effect whatsoever on the operation of the SCR and it will continue toconduct until the current is removed from its direct path as shown inFIG. 1 by opening switch No. .12. On the other hand,if a forward biaswere placed on the SCR 2, as for example, a negative polarity in theforward direction of SCR 1, then the gate condition being the same asfor SCR 1 will permit SCR 2 to conduct with SCR 1 01f: From this it canbe seen that the triac shown in FIG. 2, consisting of two siliconcontrolled rectifiers adds protection to the circuit shown in FIG. 1 byproviding a path around SCR 1 in the event there is a transient in thereverse direction which SCR 1 is not able to handle.

As is the case with most inductive devices, a sudden break in circuitcontinuity causes a reverse current to flow and even in the smallestdevices, these currents may be well beyond the limits of operation ofmany semi-conductor switches. For this and other reasons the triac isused because the reverse emf produced in the coil 15 bypasses SCR 1through SCR 2. If, for example, a single silicon controlled rectifierwere used, then the reverse current might tend to damage semi-conductor.There are, however, heavy duty devices which would be able to handlehigher current. However, the cost of such an item is rapidly increasedas the power ratings go up and as such it is undesirable for arelatively inexpensive warning device. The triac on the other hand canbe manufactured closely to the typical operating characteristics of thecircuit and not be effected by the high inverse current produced by thecollapse of the-coil field, because SCR 2 provides the reverse currentpath.

The characteristics of the triac semi-conductor provides the means forapplying the device to the apparatus shown in FIG. 1. Triac 14 acts as alatch or stick circuit, and

can be used for maintaining activation of the warning device 10, as longas power from the battery continues to flow through the main conductionpath of the triac. In other words, the only way to deenergize thewarning device is to open the contacts 12 and remove energy from thecircuit as previously noted. In many applications, a stick relay wouldnormally be used, however, such a relay requires either an externalsource of power to maintain its energized state or a larger battery,both alternatives are not particularly desirable, whereas the insertionof the triac into the circuit achieves the purpose at less cost. Thereason for requiring a latch circuit, is that in the event any of theremote switches S1 through Sn become closed, the device remainsenergized until interfered with by an observer. This requires thatunless the warning is noticed, it will continue to operate, and if anyof the particular switches S1 through Sn later open, the alarm conditionis maintained by continued energization of the warning device 10.Certain check out procedures may be required after activation of thewarning in accordance with the practices of those maintaining theapparatus.

Another advantage of the system as shown in FIG. 1 is that the triac 14may be connected without regard to polarity considerations since thebias is established by battery 11 and the triac conducts in the desireddirection because the main path directly through the triac 14 will bealways forward biased because of the inverse relationship of the SCRswhich make up the triac. This eliminates the chances of an inadvertentreverse connection.

There has therefore been provided a control circuit for a DC. warningdevice which is relatively low in cost, quite simple to manufacture andbecause of the semiconductor construction requires little power, alimited space requirement and is generally free of maintenance problems.

While there has been shown what is at present considered to be thepreferred embodiment of the invention it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention, and it is therefore aimedin the appended claims to cover all such changes and modifications thatfall within the true spirit and scope of the invention.

What is claimed is:

1. A remote control circuit for a direct current actuatedelectro-magnetic alarm apparatus including:

(a) a coil for actuating said alarm apparatus when a current equal to atleast a predetermined magnitude is passed through said coil;

(b) normally closed breaker points serially connected to the coil andopened in response to the passage of a current equal to at least saidpredetermined magnitude through said coil;

(c) an impedance element connected in parallel with the breaker pointsand having an appropriate impedance value for:

(1) maintaining circuit continuity regardless of the opened or closedcondition of the breaker points;

(2) reducing the current in said coil below a holding value thereof whensaid breaker points are open; and

(3) absorbing at least some of the inductive energy which results fromthe opening of said breaker points;

(d) alarm condition sensing means for completing a circuit in responseto the alarm condition; and

(e) a normally non-conductive triac semiconductor having its mainconduction path connected serially with the coil and with its gateelectrode coupled to the alarm condition sensing means for triggeringconduction of the triac and actuating the coil in response to saidcircuit completion.

2. A remote control circuit of claim 1 wherein said impedance is arelatively high supervisory resistor and said alarm condition sensingdevice comprises a switch activated in response to an alarm conditionfor grounding the gate of the triac.

3. The remote control circuit of claim 1 wherein said direct currentactuated electro-magnetic alarm apparatus comprises: an audible warningbell or buzzer.

References Cited UNITED STATES PATENTS 3,593,273 7/1971 Teich 340-633,594,771 7/1971 Uthene 340-276 3,517,382 6/ 1970 Stein et al. 340-228 RX 3,538,385 11/1970 Obenhaus et al. 307-305 X 3,553,641 1/1971 Moragne u340-64 3,603,947 9/1971 Schubert 340-213 R DAVID L. TRA-FTON, PrimaryExaminer US. Cl. X.R.

